In a rotary machine in which a rotation shaft is provided so as to penetrate a housing, a dry gas seal structure is widely used as a seal structure for sealing a gap between the rotation shaft and the housing (for example, refer to Japanese Unexamined Patent Application, First Publication No. 2004-190783). Here, FIG. 13 is a schematic vertical cross-sectional view showing a dry gas seal structure 70 according to an example of the related art. As shown in the drawing, the dry gas seal structure 70 includes rotation rings 72 that are fixed to a rotary shaft 71 and integrally rotate, and stationary rings 74 that are provided in a housing 73 so as to face the rotation rings 72, spiral grooves (not shown) are formed on the surfaces of the rotation rings 72, and the stationary rings 74 are pressed toward the rotation rings 72 due to coil springs 75. According to such a configuration, when the rotary shaft 71 is not rotated, the rotation rings 72 and the stationary rings 74 are in contact with each other due to the spring force of the coil springs 75. On the other hand, when the rotary shaft 71 rotates, gas in the housing 73 is introduced into the inside of the spiral groove, and small sealing gaps 76 are caused between the rotation rings 72 and the stationary rings 74 due to the resulting dynamic pressure effect. In addition, only a small amount of the gas in the housing 73 leaks outside through the small sealing gaps 76 so that the gap between the rotary shaft 71 and the housing 73 is sealed.